Biodiesel is manufactured by transesterification of animal or vegetable oils/fats. Such oils and fats comprise triglyceride esters containing long chain fatty acid moieties. In biodiesel synthesis, such triglycerides are transesterified with short chain alcohols, typically methanol and sometimes ethanol though other alcohols have been used. The reaction can be carried out in the presence of an acidic or basic catalyst and in general the basic catalysts are faster, with sodium hydroxide or potassium hydroxide being the most common. Typically, sodium hydroxide or potassium hydroxide with relatively low water level (particularly in powder or pellet form) is mixed with the alcohol, for example methanol, and then mixed with the oil.
For the commercial production of biodiesel, it is desirable to reach a relatively high degree of conversion of glyceride ester into biodiesel (preferably 96.5% or above) within a reasonable time period. In the past, it has been found that the time required to reach such a high level of conversion is comparatively long.
A problem has been encountered that basic methanol and oil do not mix very well, because of their different densities and because of the coalescing nature of their respective phases.
Conventional approaches to improving the overall kinetics having included raising the temperature, and applying large degree of shear by agitation.
For example, in the past, the transesterification reaction has been carried out in batch reactors provided with stirrers. Whilst reasonable results have been obtained with such reactors, for large scale industrial processing, a continuous system is preferred, rather than a batch process.
A pipe reactor is a suitable design of continuous reactor for the manufacture of biodiesel.
Various devices have been used in pipe reactors for providing high shear, but many of these (for example jets, mechanical mixers, oscillating flow) require high-energy input levels, which are expensive to run or involve relatively sensitive equipment. In many cases, high degrees of conversion are still not reached in a practical time span.
WO99/26913 discloses a method for production of fatty acid methyl ester in which a static mixer is used which creates high or powerful turbulence. There is a substantial pressure drop across the static mixer. This requires very high pressures to operate, which is uneconomic.